In order to deal with a recent sharp increase in an amount of radio communication, use of a Multi Input Multi Output (MIMO) communication system in which a plurality of antennas are concurrently used, beam forming by an array antenna in which a plurality of antennas are arranged and the like has been advancing and the number of antennas mounted on a radio communication apparatus has tended to increase. It is therefore strongly required that both a decrease in the size of the antenna mounted on the radio communication apparatus and a reduction in the cost of the antenna be achieved.
A dipole antenna which has high radiation efficiency and is capable of radiating radio waves in a wide range of directions and a patch antenna that can be formed to be thin are well known as two of the most common antennas. However, it is difficult to reduce the respective sizes of these antennas since they each need to have a size of a half of the wavelength in principle.
Patent Literature 1 discloses a technique for reducing the size of an antenna by adding a parasitic element, a part of which is formed of magnetic materials, to a dipole antenna. In Patent Literature 1, by controlling the distribution of magnetic field lines in the vicinity of the antenna using magnetic materials, it is possible to reduce the size of the antenna and perform impedance matching without using a matching circuit.
Further, Non-Patent Literature 1 discloses a technique for arranging multiple artificial magnetic elements called split-ring resonators inside a patch antenna. By increasing the effective permeability inside the patch antenna by the split-ring resonators, it is possible to shorten the wavelength and to reduce the size of the antenna.